Chimeric proteins comprising a Vpr/Vpx virion incorporation domain for targeting into HIV-1 or HIV-2 virions

ABSTRACT

The present invention is directed toward chimeric human immunodeficiency virus type 1 and 2 (HIV-1 and -2) proteins that are capable of being incorporated into the virion when expressed in trans. These chimeric proteins consist of a first portion comprising an HIV-1 or HIV-2 Vpr/Vpx virion incorporation domain which includes the predicted N-terminal alpha helix. This domain is capable of interacting with the p6 domain of the Pr55 gag . The second portion of the chimera comprises a sequence containing RNase activity, protease activity, or a domain capable of inhibiting virion morphogenesis and assembly. The disclosed invention provides a chimera that affects the structural organization or functional integrity of the mature virion by enzymatic disturbance or steric hindrance of the virion.

BACKGROUND OF THE INVENTION

(a) Field of the Invention

The invention relates to two different approaches using the Vpr/Vpx protein or p6 protein for treatment of HIV-1 and HIV-2 infections.

(b) Description of Prior Art

Acquired Immune Deficiency Syndrome (AIDS) is a slow degenerative disease of the immune and nervous systems caused by the Human Immunodeficiency Virus (HIV). The life cycle of HIV lies at the heart of the AIDS pandemic. The spread of the disease is primarily determined by the infectious properties of this virus. Progressive lethal degeneration of the immune and central nervous systems results from long term chronic replication of this virus.

HIV belongs to a unique virus family, the retroviridae, a group of small, enveloped, positive stranded, RNA viruses (Lavallee et al., 1994, J. Virol., 68:1926-1934; International Patent Application No. WO 90/158,75 on Dec. 27, 1990 in the name of DANA FARBER CANCER INSTITUTE). These viruses code for an enzyme, the reverse transcriptase, which enables them to replicate their RNA genome through a DNA intermediate. Simple retroviruses contain three, contiguous reading frames coding for the gag, pol and env genes, which constitute their structural and enzymatic repertoire, all packaged in the progeny virion. The gag and env genes encode the core nucleocapsids proteins and the membrane glycoproteins of the virus, respectively, whereas the pol gene gives rise to the reverse transcriptase and other enzymatic activities (ribonuclease H, integrase and protease) that are essential for viral replication. HIV belongs to the lentivirus subfamily, members of which are characterized by several additional open reading frames (ORF) not found in simple retroviruses (FIG. 1). These ORFS all appear following gag-pol sequences, either immediately preceding the env sequences or overlapping it, and at least in one case, nef, extending well into the 3' Long Terminal Repeat (LTR). These ORFs code for non-structural viral proteins readily detectable in the cells. Much evidence has accumulated indicating that these gene products, collectively referred to as auxiliary proteins, are capable of modulating viral replication and infectivity.

HIV-1 possesses at least six such auxiliary proteins, namely, Vif, Vpr, Tat, Rev, Vpu and Nef. The closely related HIV-2 does not code for Vpu, but codes for another unrelated protein, Vpx, not found in HIV-1. Mutations affecting either Tat or Rev severely impair viral replication indicating that these two auxiliary proteins are essential for viral replication. However, at least in vitro, mutations affecting other auxiliary proteins result in minimal effect on the viral replication kinetics. Hence, these proteins have been dubbed dispensable or non-essential for in vitro replication, and are usually referred to as accessory gene products.

In the past few years, it has become evident that while these "accessory" genes are not required for productive replication, they are nonetheless capable of affecting replication events, even in vitro. More importantly, recent data indicates that they may affect pathogenesis in vivo.

The vpr gene encodes a 14 kDa protein (96 amino acids) in most strains of HIV-1 (FIG. 2; Myers et al., 1993, Human Retroviruses and AIDS 1993 I-II, Los Alamos National Laboratory, New Mexico, USA), although the open reading frame is often truncated in viral strains extensively passaged in tissue culture. The vpr open reading frame is also present in HIV-2 isolates and in most but not in all SIV isolates. A sequence similar to HIV-1 vpr is also found in Visna virus. Recent amino acid comparison between HIV-2 vpr and vpx showed regions of similarity suggesting that vpx in the HIV-2/SIV group may have arisen by duplication of the vpr gene (FIG. 2; Myers et al., 1993, Human Retroviruses and AIDS 1993 I-II, Los Alamos National Laboratory, New Mexico, USA). The Vpr protein is made from a singly spliced rev-dependent mRNA species that accumulates late in infection. The vpr protein of HIV and SIV have recently been shown to be present in mature viral particles in multiple copies. Interestingly, Vpr and Vpx are the first regulatory protein of any retrovirus found to be associated with viral particles. Other regulatory proteins, such as tat, Rev, Nef, Vif and Vpu are not virion-associated. The assembly and maturation of HIV-1 viral particles is a complex process in which the structural Gag, Pol and Env gene products are expressed in the form of polyprotein precursors. The Gag proteins of HIV play a central role in virion assembly and budding. Gag proteins are initially synthesized as myristylated polyprotein precursors, Pr55^(gag) and Pr160^(gag-pol), which are transported to the inner face of the plasma membrane where they can direct particle formation, even in the absence of other viral proteins. Complete budding leads to formation of immature particles, followed by HIV protease mediated cleavage of the Gag and Gag-Pol precursor polyproteins and formation of mature HIV particles with condensed core. The mature virion proteins derived from cleavage of the gag-encoded precursor, pr55^(gag), include the p17 matrix protein (MA), the p24 capsid protein (CA), the p7 nucleocapsid protein (NC), and a small proline-rich peptide of approximately 6 kDa designated p6 which are linked in this order in the polyprotein precursor. Vpr is not part of the virus polyprotein precursors and its incorporation occurs by way of an interaction with a component normally found in the viral particle. It was recently reported that the HIV-1 Vpr could be incorporated in trans into viral-like particle (VLP) originating front expression of the pr55^(gag) only (Lavallee et al., 1994, J. Virol., 68:1926-1934). Data from this and other studies indicate that Vpr incorporation appeared to result from a direct interaction of Vpr with the carboxy-terminal region of the Pr55^(gag) polyprotein (Paxton et al., 1993, Journal of Virology, 67(12):7229-7237; Lu et al., 1993, Journal of Virology, 67(1):6542-6550).

Functional studies indicated that the full length vpr protein could confer favorable growth properties to viruses. The increase in virion production is more pronounced in primary macrophages in both HIV-1 and HIV-2 systems, suggesting that Vpr function may be important in specific target cells. Interestingly, while mutations affecting HIV-1 vpr do not affect replication in peripheral blood mononuclear cells (PBMC), mutations in HIV-2 vpr results in a measurable impairment in these cells. Similarly, a recent study using anti-sense RNA directed against vpr inhibited viral replication in primary macrophages but not in transformed T-cells. Previous work indicated that this rapid growth advantage may be conferred by the weak transactivation property of Vpr on HIV-LTR directed gene expression (European Patent Application published under No. 474,797 on Mar. 18, 1992 in the name of DANA FARBER CANCER INSTITUTE). Cotransfection experiments suggest that vpr could augment the expression of a reporter gene from several heterologous promoters by approximately three to ten fold.

The carboxyl terminal sequence of Vpr have been shown to be important for Vpr mediated transactivation as prematurely truncated proteins are non-functional and are not packaged into the virion. Interestingly, a recent report also indicated that the carboxyl terminal of the protein is important for nuclear localization (Lu et al., 1993, Journal of Virology, 67(1):6542-6550). A specific vpr responsive LTR sequence was not identified and the exact mechanism by which vpr augments reporter gene expression is not clear. The precise mode of action of vpr is yet to be established. However, the presence of vpr in the viral particle suggests that this protein has a role in the early stage of infection. Virion-associated non-structural proteins in many viral systems play a pivotal enzymatic functions in early replication steps, either because cellular homologues are unavailable or are sequestered, for example, in the nucleus. It is possible that Vpr is one such protein, capable of modulating early viral specific functions such as reverse transcription stabilization of early RNA or DNA intermediates, transport to the nucleus or integration. It is equally possible that Vpr could function at an early step, in a non-viral specific manner, by triggering processes that could make the cellular environment congenial to establish viral infection. In this regard, HIV-1 Vpr has been reported to be involved in inducing cellular differentiation in rhabdomyosarcoma cells (Levy et al., 1993, Cell, 72:541-550). Finally, because Vpr is synthesized late in the infection cycle of HIV, it may regulate the morphogenesis of the virus (late events) by an unknown mechanism or constitute a structural protein involved in the integrity of the virions.

The use of transport polypeptides for biological targeting is well known and was adapted to many fields. The HIV Tat protein has been described to effect the delivery of molecules into the cytoplasm and nuclei of cells (International Application published on Mar. 3, 1994 as No. WO 94/04686 in the name of BIOGEN, INC.). However, the Tat transport polypeptides can not allow the delivery of molecules to HIV virions. Viral proteins such as Gag of Rous sarcoma virus and Moloney murine leukemia virus and portion of HIV-1 Gag protein have been used as carrier for incorporation of foreign antigens and enzymatic markers into retroviral particles (Wagner et al., 1994, Virology, 200:162-175). However, most of the Gag protein sequences are essential for efficient viral particles assembly, thus limiting the use of such virion components as carrier.

It would be highly desirable to be provided with means to target molecules to mature HIV-1 and HIV-2 virions to affect their structural organization and/or functional integrity.

It would also be highly desirable to be provided with a Vpr protein, a Vpx protein or fragments thereof which permit the development of chimeric molecules that can be specifically targeted into the mature HIV-1 and HIV-2 virions to affect their structural organization and/or functional integrity, thereby resulting in treatment of HIV-1 and HIV-2 infections.

It would also be highly desirable to be provided with a therapeutic agent which permit the targeting of chimeric molecules into the mature HIV-1 and HIV-2 virions as a treatment for HIV-1 and HIV-2 infections.

It would also be highly desirable to be provided with the identification of the protein interaction responsible for Vpr or Vpx incorporation in the mature HIV-1 and HIV-2 virions.

It would also be highly desirable to be provided with means to target the protein interaction responsible for Vpr or Vpx incorporation in the mature HIV-1 and HIV-2 virions to affect their functional integrity.

It would also be highly desirable to be provided with a Vpr protein fragment, a Vpx protein fragment, a p6 protein or p6 protein fragment which permits the development of molecules that can specifically interfere with the protein interaction responsible for Vpr or Vpx incorporation in the mature HIV-1 and HIV-2 virions to affect their functional integrity, thereby resulting in treatment of HIV-1 and HIV-2 infections.

It would also be highly desirable to be provided with a therapeutic agent which interferes with the protein interaction responsible for Vpr or Vpx incorporation in the mature HIV-1 and HIV-2 virions as a treatment for HIV-1 and HIV-2 infections.

SUMMARY OF THE INVENTION

One aim of the present invention is to provide a means to target molecules to mature HIV-1 and HIV-2 virions to affect their structural organization and/or functional integrity.

Another aim of the present invention is to provide a Vpr protein, a Vpx protein or fragments thereof which permit the development of chimeric molecules that can be specifically targeted into the mature HIV-1 and HIV-2 virions to affect their structural organization and/or functional integrity, thereby resulting in treatment of HIV-1 and HIV-2 infections.

Another aim of the present invention is to provide a therapeutic agent which permit the targeting of chimeric molecules into the mature HIV-1 and HIV-2 virions as a treatment for HIV-1 and HIV-2 infections.

Another aim of the present invention is to provide the identification of the protein interaction responsible for Vpr or Vpx incorporation in the mature HIV-1 and HIV-2 virions.

Another aim of the present invention is to provide means to target the protein interaction responsible for Vpr or Vpx incorporation in the mature HIV-1 and HIV-2 virions to affect their functional integrity.

Another aim of the present invention is to provide a Vpr protein fragment, a Vpx protein fragment, a p6 protein or a p6 protein fragment which permits the development of molecules that can specifically interfere with the protein interaction responsible for Vpr or Vpx incorporation in the mature HIV-1 and HIV-2 virions to affect their functional integrity, thereby resulting in treatment of HIV-1 and HIV-2 infections.

Another aim of the present invention is to provide a therapeutic agent which interferes with the protein interaction responsible for Vpr or Vpx incorporation in the mature HIV-1 and HIV-2 virions as a treatment for HIV-1 and HIV-2 infections.

In accordance with the present invention there is provided a protein for targeting into a mature HIV-1 or HIV-2 virion, which comprises a sufficient number of amino acids of a Vpr protein, a Vpx protein, functional derivatives or fragments thereof, wherein the protein interacts with at Gag-precursor protein of the mature virion and is incorporated by the virion. More specifically, the protein interacts with the protein p6 which is a component of the Gag-precursor protein.

More specifically, the protein of the present invention, further comprises a protein fragment covalently attached to its N- or C-terminal to form a chimera protein which is also incorporated by the mature virion. Such an attached protein fragment of the present invention consists of amino acid sequences having RNase, protease activities or amino acid sequences capable of creating steric hindrance during virion morphogenesis.

More specifically, the protein of the present invention, further comprises a molecule to form a protein-molecule complex which is also incorporated by the mature virion. Such a molecule is selected from the group consisting of anti-viral agents, Rnases, proteases, and amino acid sequences capable of creating steric hindrance during virion morphogenesis. The molecule of the protein-molecule complex of the present invention affects the structural organization or functional integrity of the mature virion by steric hindrance or enzymatic disturbance of the virion.

In accordance with the present invention there is also provided a protein which interferes with Vpr or Vpx incorporation into HIV-1 and HIV-2 virions and which comprises a sufficient number of amino acids of a Vpr protein fragment, a Vpx protein fragment, a p6 protein, p6 protein fragment, or its functional derivative thereof, wherein the protein interacts either with Gag-precursor or with Vpr or Vpx protein to compete with the Vpr-Gag-precursor or Vpx-Gag-precursor interaction and consequently to interfere with the incorporation of the native Vpr into the virions and to substantially prevent replication of the mature virion.

In accordance with the present invention there is also provided a method of substantially reducing HIV expression or replication in a patient infected with HIV-1 or HIV-2, which comprises administering at least one therapeutic agent selected from the group consisting of the protein or DNA sequences encoding the protein of the present invention, to the patient in association with a pharmaceutically acceptable carrier. The administration step of the method is effected intracellularly for anti-viral treatment including gene therapy or immunization of the patient or by DNA transfection of the patient's hematopoietic cells followed by readministration of the transfected cells.

Accordingly, in view of two different approaches of the present invention, therapeutic agents which may be used in accordance with the present invention are selected from the group consisting of a protein of the present invention including Vpr/Vpx chimeric proteins comprising RNase, proteases or amino acids sequences capable of creating steric hindrance during virion morphogenesis, Vpr/Vpx protein fragment, p6 protein and p6 protein fragment, and DNA sequences encoding a protein of the present invention.

In accordance with the present invention there is also provided a pharmaceutical composition for reducing HIV expression in a patient infected with HIV-1 or HIV-2, which comprises a sufficient amount of the therapeutic agent of the present invention in association with a pharmaceutically acceptable carrier.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the HIV genetic organization, where the vpr gene is positioned in the central region;

FIG. 2 shows the amino acid sequences of native Vpr protein from HIVLAI isolate and native Vpr and Vpx proteins from HIV2ROD isolate;

FIG. 3 shows the mutagenesis chart of the vpr gene of HxBH10 or pHxBRU template of HIV-1;

FIGS. 4A, 4B, and 4C show the analysis of Vpr present in lysates and supernatants of MT4 cells infected with HIV-1 containing various mutated or truncated vpr mutants;

FIG. 5 shows the stability of the truncated or mutated Vpr protein in infected MT4 cells;

FIG. 6 shows quantification of the incorporation of different mutated Vpr into HIV-1 virions;

FIGS. 7A and 7B show the expression plasmids and the P6 construct plasmid expressing P6 mutant;

FIG. 8 shows the incorporation of Vpr into virions in the presence of different truncated or mutated Gag P6 protein;

FIG. 9 shows the construction of a vector expressing a chimera protein between Vpr from HIV-1 Eli strain and a portion of the HIV-1 Vpu protein;

FIG. 10 shows the analysis of Vpr-Vpu chimera present in lysates and pelleted viral particles from COS cells co-transfected with the Vpr-Vpu expresser of FIG. 9 and a HIV-1 vpr-minus infectious molecular clone; and

FIG. 11 shows the construction of a chimera protein between Vpr and a portion of the HIV-1 Vpu in the HIV-1 SVC21 BRU strain.

DETAILED DESCRIPTION OF THE INVENTION

In accordance with the present invention, two different approaches using the Vpr/Vpx protein and p6 protein are described herein for the treatment of HIV-1 and HIV-2 infections.

In the first approach, the region of Vpr/Vpx protein, which is involved in the protein interaction responsible for Vpr/Vpx virion-incorporation, is used as a carrier to target molecules to mature HIV-1 and HIV-2 virions.

In the second approach, the region of Vpr/Vpx protein or alternatively the region of Gag-precursor, which are both involved in the protein interaction responsible for Vpr/Vpx virion-incorporation, is used to interfere with the native viral Vpr/Vpx protein incorporation.

In general, the abbreviations used herein for designating the amino acids are based on recommendations of the IUPAC-IUB commission on Biochemical Nomenclature (Biochemistry, 1972, 11:1726-1732).

In accordance with the first approach of the present invention, there is provided the use of the Vpr or Vpx protein, which is referred to as the "Vpr/Vpx" protein, functional derivatives or fragments thereof for the targeting of molecules to the HIV-1 and HIV-2 virions.

The preferred Vpr/Vpx protein, which is used in accordance with the first approach of the present invention, contains a sufficient number of amino acids corresponding to at least one of the following amino acid sequences consisting of: ##STR1## functional fragments or derivatives thereof, wherein the Vpr/Vpx protein, its fragments or derivatives thereof have retained the virion-incorporation function of the native Vpr/Vpx protein.

The expression "functional fragments or derivatives" when used herein is intended to mean any substitutions, deletions and/or additions of amino acids that do not affect the virion-incorporation function of the Vpr native protein.

In accordance with the first approach of the present invention, a preferred Vpr/Vpx chimera protein comprises an amino acid sequence of a Vpr/Vpx protein or a functional derivative thereof and a molecule attached to the amino acid sequence. Said molecule may be covalently attached at the N- or C-terminal of the amino acid sequence or it may be attached to the amino acid sequence at any amino acid position by chemical cross-linking or by genetic fusion.

A preferred molecule used in accordance with the present invention may be selected from the group consisting of an anti-viral agent and a second amino acid sequence which contains a sufficient number of amino acids corresponding to RNase, proteases, or any protein capable of creating steric hindrance during virion morphogenesis.

The Vpr/Vpx chimera protein in accordance with the first approach of the present invention may be used for the targeting of molecules into the mature virions of HIV-1 and HIV-2, such as polypeptides, proteins and anti-viral agents, among others.

In accordance with the second approach of the present invention, there is provided the use of Vpr/Vpx protein fragments, p6 protein, p6 protein fragment, or functional derivatives thereof which interfere with the native Vpr/Vpx incorporation into HIV-1 and HIV-2 virions. Again, the Vpr/Vpx protein fragments, p6 protein, p6 protein fragments, or functional derivatives thereof have retained their ability to interact with the native Vpr/Vpx or p6 protein, respectively. The expression "functional derivatives" when used herein is intended to mean any substitutions, deletions and/or additions of amino acids that do not affect the virion-incorporation function of the native Vpr/Vpx or p6 protein.

The preferred Vpr/Vpx protein fragments which is used in accordance with the second approach of the present invention is a fragment of the following amino acid sequence consisting of: ##STR2## wherein said fragment is a region of the Vpr/Vpx protein which binds to Gag-precursor.

The preferred p6 protein which is used in accordance with the second approach of the present invention contains a sufficient number of amino acids corresponding to the following amino acid sequences consisting of: ##STR3##

The Vpr/Vpx fragment, p6 protein and p6 protein fragment in accordance with the second approach of the present invention may be used for interfering with the virion-incorporation of native Vpr/Vpx into HIV-1 and HIV-2 virions.

The purpose of the treatment in accordance with the first and second approaches of the present invention may be a prevention or a treatment. The product in these treatment procedures may be expressed intracellularly or provided to the cell via the blood stream.

In accordance with the first approach of the present invention, the expressed product may be effective in the production of defective viral particles, for instance, viral particles with Vpr/Vpx chimera proteins such as the ones associated with virally directed protease or nuclease or with a portion of protein which affects the structural organization and/or functional integrity of the virions.

The treatment in accordance with the second approach of the present invention may consists in the production of viral particles having substantially reduced replication capacity, for instance, HIV-1 and HIV-2 viral particles devoided of functional level of Vpr/Vpx protein as a consequence of Vpr-Gag-precursor or Vpx-Gag-precursor interaction interference using Vpr/Vpx protein fragments, p6 protein and p6 protein fragments.

HIV-1 vpr Regions Associated With Vital Particles Incorporation

The substitution mutations and deletions of vpr were generated by site-directed mutagenesis. Wildtype vpr sequence and location of predicted alpha-helix structures are indicated at the top of FIG. 3. Oligonucleotide-directed mutagenesis of the vpr gene was carried out on DNA fragments derived from pHxBRU template (FIG. 3) and then cloned into an infectious provirus (pHxBRU) (Lavallee et al., 1994, J. Virol., 68:1926-1934). Amino acid substitutions are indicated. BRUR 77/79, BRUR 76/79 and HxBH10 72/78 (Yao et al., 1992, Journal of Virology, 66(8):5119-5126) are truncated vpr proteins with additional unrelated amino acids generated by frame shift mutations.

FIGS. 4A, 4B and 4C are autoradiograms that illustrate the analysis of truncated or substituted Vpr mutants in HIV-1 infected MT4 cells. 2×10⁶ T-lymphoid cells (MT4) were infected (or transfected, FIG. 4C) with HIV-1 which contain wildtype or truncated Vpr (FIG. 3), as indicated at the top of the autoradiograms. The position of HIV-1 viral proteins are indicated at the left of the autoradiograms (Vpr). At 40 h post-transfection, cells were labelled with 100 μCi of ³⁵ S-methionine and 100 μCi of ³ H-leucine for 16 h. Virions were pelleted from cell-free supernatants by ultracentrifugation at 35,000 rpm through a 20% Sucrose cushion for 2 h. Both cells (left panel) and sucrose cushion pelleted viruses (right panel, FIGS. 4A, 4B & 4C) were lyzed in RIPA buffer (140 mM NaCl, 8 mM NaHPO₄, 2 mM NaH₂ PO₄, 1% Nonidet™ P-40, 0.5%. sodium deoxycholate, 0.05% SDS) and immunoprecipitated with a HIV-1 positive human serum combined with a rabbit anti-Vpr serum. Proteins were then analyzed on a sodium dodecyl sulfate (SDS) 12.5%-17% gradient polyacrylamide gel electrophoresis (PAGE) and autoradiography. Quantification of virion associated vpr and protein stability was determined by densitometric scanning of the autoradiograms using a laser densitometer (Molecular Dynamics™ densitometer).

FIG. 5 shows the stability of different truncated (FIG. 5B) or substituted (FIG. 5A) Vpr mutants in HIV-1 infected cell lysates. The intensity of wildtype or mutated Vpr proteins were quantified relative to the intensity of the p66 reverse transcriptase (RT) bands. Immunoprecipitation analysis has shown that all truncated Vpr proteins were present at low level in cell lysates suggesting the importance of the C-terminal region for Vpr stability (FIGS. 4A and 5B).

FIG. 6 shows the efficiency of incorporation of different mutated Vpr into HIV-1 virions. The incorporation of mutated Vpr into virions was also evaluated by densitometric analysis. The intensity of Vpr proteins into virions were quantified relative to the intensity of the p66 reverse transcriptase (RT) bands in autoradiograms presented in FIGS. 4B and 4C. The results of the present invention demonstrate that substitution mutations (A30F, H331 and E25K) in the N-terminal portion of vpr significantly impair the incorporation of vpr protein into virions (FIGS. 4B, 4C and 6). Interestingly, this region of the protein is predicted to form an alpha helix conformation which is reminiscent of a structure involved in protein-protein interaction. These data indicate that the N-terminus of Vpr is important for vpr incorporation in the virion. This region will be further defined by analyzing additional vpr mutants for their stability and virion-incorporation capacity.

HIV-1 GAG P6 Regions Associated With Vpr Incorporation

To investigate the mechanism of incorporation of Vpr, the ability of Gag-expressor plasmids, harboring deletions or mutations in the C-terminus of the capsid precursor, to target Vpr into virions in transiently transfected cells was tested. In this system two expresser plasmids described in FIG. 7A were cotransfected into COS-7 cells (Lavallee et al., 1994, J. Virol., 68:1926-1934; FIG. 7A). Deletions are shown as dotted lines between the thick lines. ptrENV contains 3109 (nucleotides 989 to 4098) and 1294 (nucleotides 5925 to 7219) base pair deletions affecting respectively gag, pol and the gp120 domain of env genes. ptrENV encodes Vpr as well as all HIV-1 auxilliary proteins (Vif, Tat, Rev, Vpu Nef and gp41). The pIIIgagCAR plasmid, a rev-dependent Gag expressor, which encodes Pr55^(gag) and the protease domain of the pol gene (PR), contains the Rev-responsive element (RRE/CAR) sequence. P6 is the C-terminal components of the Pr55^(gag) precursor (FIG. 7A). FIG. 7B illustrates the P6 constructs. Plasmids expressing P6 mutant were generated by introducing a termination codon or a substitution by polymerase chain reaction (PCR)-based site-directed mutagenesis in pIIIgagCAR plasmid.

FIG. 8 illustates the trans incorporation of Vpr into virus-like particles. COS-7 sells were transfected with pIIIgagCAR plasmid (lane 1), or ptrENV plasmid (lane 2) or cotransfected with both constructs (lane 3). ptrENV was cotransfected with pIIIgagCAR based construct harboring a substitution or a premature termination codon in the p6 protein: L1/stop (lane 4), S17/stop (lane 5), Y36/stop (lane 6), P10,11L (lane 7), L44/stop (lane 8), P49/stop (lane 9). 48 h posttransfection ³⁵ S!methionine- and ³ H!leucine-labelled viral proteins were immunoprecipitated, from the cell lysates or the cell-free supernatant centrifuged through a 20% sucrose cushion, with the HIV-1 positive human serum 162 mixed with a rabbit anti-Vpr polyclonal antibodies and analysed by SDS-PAGE and autoradiography.

The 14kDa vpr product can be detected in the pelleted virions produced by cells cotransfected with pIIIgagCAR and ptrENV or the P49/stop or P10,11L mutants (FIG. 8, right panel, lanes 3, 9 and 7, respectively). However, virions produced from cells cotransfected in the presence of ptrENV and L1/stop, S17/stop, Y36/stop or L44/stop constructs lacked detectable Vpr (lanes 4, 5, 6 and 8, respectively). These results indicate a direct correlation between the absence of p6 and the loss of Vpr incorporation, suggesting that p6 is directly implicated. Moreover, deletion analysis suggests that the carboxyl terminal of p6 is important for Vpr incorporation. Indeed, a very short region corresponding to amino acid 45 to 48 inclusively (FGND) is critical for Vpr incorporation.

The present invention will be more readily understood by referring to the following examples which are given to illustrate the invention rather than to limit its scope.

EXAMPLE I Incorporation in Trans of a Specific Epitope into Retroviral Particles

The ability of foreign antigen to be incorporated in trans into viral particles when fused to Vpr protein was examined. A vector which expresses a fusion protein containing the first 93 amino acids of Vpr from the Eli Strain and a Vpu epitope was constructed (FIG. 9). The last 18 C-terminal amino acids of Vpu which contain a specific epitope (Cohen et al., 1988, Nature, 334:532-534) has been cloned at the BamHI restriction site located at the 3' end of the Vpr sequence. The chimera protein is under the control of the cytomegalovirus (CMV) promoter (Lavallee et al., 1994, J. Virol., 68:1926-1934).

FIG. 10 shows the incorporation of Vpr-Vpu chimera into HIV-1 virions. One million COS-7 cells were cotransfected with the SVCMV-Vpr-Vpu chimera expressor and with a HIV-1 Vpr minus infectious molecular clone (pHxBRU-RATG⁻). This HIV-1 clone was generated by introducing a GTG codon instead of the ATG initiation codon in the Vpr gene from the pHxBRU proviral clone (Lavallee et al., 1994, J. Virol., 68:1926-1934). 48 h post-transfection, cells were labelled with 200 μCi of ³⁵ S-methionine and 200 μCi of ³ H-leucine for 16 h. Virions were pelleted from the cell-free supernatants by ultracentrifugation at 35,000 rpm through a 20% sucrose cushion for 2 h. Both cells (left panel) and sucrose cushion pelleted viruses (right panel) were lyzed in RIPA buffer (140 mM NaCl, 8 mM NaHPO₄, 2 mM NaH₂ PO₄, 1% Nonidet™ P-40, 0.5% sodium deoxycholate, 0.05% SDS) and immunoprecipitated with a HIV-1 positive human serum combined with a rabbit anti-Vpr serum or with a rabbit anti-Vpu serum as indicated at the top of each lane of FIG. 10. The position of HIV-1 viral proteins are indicated at the left of the gel. Analysis of vpr products in the cell lysates and supernatants has revealed that 1) Vpr-Vpu chimera is stably expressed in transfected cells and 2) both Vpu (λVpu) and Vpr (λvpr) antisera are able to immunoprecipitate the chimera product from the virions (FIG. 10). These data indicate that the Vpu epitope was successfully transferred into virions when expressed in trans as a Vpr fusion product.

EXAMPLE II Incorporation of a Specific Epitope into Retroviral Particles From a HIV-1 Cloned Provirus

Trans-incorporation of Vpr chimera protein into Vpr-virion In MT4 cells presents limitations due to the low transfection efficiency-obtained when two expression vectors are transfected in T cell lines. To address this question, a Vpr-Vpu fusion protein was cloned into a Vpu-minus HIV-1 provirus plasmid. FIG. 11 shows a schematic representation of the proviral form of the retrovirus construct pHxBRU vprIE which encodes the Vpr sequence from pHxBRU (Lavallee et al., 1994, J. Virol., 68:1926-1934) fused to an immunodominant epitope tag corresponding to the last 18 amino acids of the BH10 Vpu-protein. This Vpu epitope is recognized by the specific Rabbit anti-Vpu peptide serum described by (Cohen et al., 1988, Nature, 334:532-534). This construction will be transfected in MT4 cells and the incorporation of the Vpr-Vpu fusion protein into virions will be measured. The introduction of a unique XbaI site at position 5410 in this construction without Vpu sequence. Vpr (pHxBRU RX) has also been designed to provide a unique cloning site in which any foreign DNA sequence could easily be covalently attached to the C-terminal end of Vpr.

The targeting of different Vpr fusion proteins in proviruses and their effects on viral replication and infectivity will further be tested in MT4 and Jurkat cell lines.

EXAMPLE III Construction of Vpr Chimeric Molecules

Chimeric molecules are developed by fusion of Vpr sequences with either sequences encoding different enzymatic activities or random amino acid sequences of different lengths. To demonstrate that large molecules and functional enzymatic activities can be efficiently transferred into virions, Vpr is fused to prokaryotic genes such as β-galactosidase, luciferase or chloramphenicol acetyltransferase to generate Vpr chimeras. Rapid, sensitive and reproducible assays have been extensively described to measure the activity of these enzymes. COS cells are co-transfected with different chimera expressors and with Vpr-minus proviruses. Incorporation and enzymatic activities of fusion proteins associated to the viral particles is measured.

Vpr covalently attached to nuclease, protease or to peptide sequence of various length (vpr-steric hindrance peptide) are also constructed and the effect of these fusion proteins on the replication and infectivity of HIV in T cells are determined. Vpr chimera proteins are tested in two different systems to measure the effect of cis and trans expression; 1) the chimera proteins are cloned into the pHxBRU RX construction (described in Example II) and are transfected into MT4 CD4+ cells (cis expression); and 2) the chimera proteins cloned into-expressors are co-transfected with a vpr-minus provirus into COS cells (trans expression). In both cases, viral production is monitored. Degradation of viral RNA or proteins in the viral particles will lead to the production of defective virions. Incorporation of Vpr chimera which affect the structure and/or the organization of the HIV virion will affect its infectious properties.

While the invention has been described in connection with specific embodiments thereof, it will be understood that it is capable of further modifications and this application is intended to cover any variations, uses, or adaptations of the invention following, in general, the principles of the invention and including such departures from the present disclosure as come within known or customary practice within the art to which the invention pertains and as may be applied to the essential features hereinbefore set forth, and as follows in the scope of the appended claims.

    __________________________________________________________________________     SEQUENCE LISTING     (1) GENERAL INFORMATION:     (iii) NUMBER OF SEQUENCES: 5     (2) INFORMATION FOR SEQ ID NO:1:     (i) SEQUENCE CHARACTERISTICS:     (A) LENGTH: 96 amino acids     (B) TYPE: amino acid     (C) STRANDEDNESS: single     (D) TOPOLOGY: linear     (ii) MOLECULE TYPE: protein     (iii) HYPOTHETICAL: NO     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:1:     MetGluGlnAlaProGluAspGlnGlyProGlnArgGluProHisAsn     151015     GluTrpThrLeuGluLeuLeuGluGluLeuLysAsnGluAlaValArg     202530     HisPheProArgIleTrpLeuHisGlyLeuGlyGlnHisIleTyrGlu     354045     ThrTyrGlyAspThrTrpAlaGlyValGluAlaIleIleArgIleLeu     505560     GlnGlnLeuLeuPheIleHisPheArgIleGlyCysArgHisSerArg     65707580     IleGlyValThrGlnGlnArgArgAlaArgAsnGlyAlaSerArgSer     859095     (2) INFORMATION FOR SEQ ID NO:2:     (i) SEQUENCE CHARACTERISTICS:     (A) LENGTH: 105 amino acids     (B) TYPE: amino acid     (C) STRANDEDNESS: single     (D) TOPOLOGY: linear     (ii) MOLECULE TYPE: protein     (iii) HYPOTHETICAL: NO     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:2:     MetAlaGluAlaProThrGluLeuProProValAspGlyThrProLeu     151015     ArgGluProGlyAspGluTrpIleIleGluIleLeuArgGluIleLys     202530     GluGluAlaLeuLysHisPheAspProArgLeuLeuIleAlaLeuGly     354045     LysTyrIleTyrThrArgHisGlyAspThrLeuGluGlyAlaArgGlu     505560     LeuIleLysValLeuGlnArgAlaLeuPheThrHisPheArgAlaGly     65707580     CysGlyHisSerArgIleGlyGlnThrArgGlyGlyAsnProLeuSer     859095     AlaIleProThrProArgAsnMetGln     100105     (2) INFORMATION FOR SEQ ID NO:3:     (i) SEQUENCE CHARACTERISTICS:     (A) LENGTH: 112 amino acids     (B) TYPE: amino acid     (C) STRANDEDNESS: single     (D) TOPOLOGY: linear     (ii) MOLECULE TYPE: protein     (iii) HYPOTHETICAL: NO     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:3:     MetThrAspProArgGluThrValProProGlyAsnSerGlyGluGlu     151015     ThrIleGlyGluAlaPheAlaTrpLeuAsnArgThrValGluAlaIle     202530     AsnArgGluAlaValAsnHisLeuProArgGluLeuIlePheGlnVal     354045     TrpGlnArgSerTrpArgTyrTrpHisAspGluGlnGlyMetSerGlu     505560     SerTyrThrLysTyrArgTyrLeuCysIleIleGlnLysAlaValTyr     65707580     MetHisValArgLysGlyCysThrCysLeuGlyArgGlyHisGlyPro     859095     GlyGlyTrpArgProGlyProProProProProProProGlyLeuVal     100105110     (2) INFORMATION FOR SEQ ID NO:4:     (i) SEQUENCE CHARACTERISTICS:     (A) LENGTH: 72 amino acids     (B) TYPE: amino acid     (C) STRANDEDNESS: single     (D) TOPOLOGY: linear     (ii) MOLECULE TYPE: protein     (iii) HYPOTHETICAL: NO     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:4:     MetGluGlnAlaProGluAspGlnGlyProGlnArgGluProHisAsn     151015     GluTrpThrLeuGluLeuLeuGluGluLeuLysAsnGluAlaValArg     202530     HisPheProArgIleTrpLeuHisGlyLeuGlyGlnHisIleTyrGlu     354045     ThrTyrGlyAspThrTrpAlaGlyValGluAlaIleIleArgIleLeu     505560     GlnGlnLeuLeuPheIleHisPhe     6570     (2) INFORMATION FOR SEQ ID NO:5:     (i) SEQUENCE CHARACTERISTICS:     (A) LENGTH: 52 amino acids     (B) TYPE: amino acid     (C) STRANDEDNESS: single     (D) TOPOLOGY: linear     (ii) MOLECULE TYPE: protein     (iii) HYPOTHETICAL: NO     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:5:     LeuGlnArgSerProGluProThrAlaProProGluGluSerPheArg     151015     SerGlyValGluThrThrThrProProGlnLysGlnGluProIleAsp     202530     LysGluLeuTyrProLeuThrSerLeuArgSerLeuPheGlyAsnAsp     354045     ProSerSerGln     50     __________________________________________________________________________ 

We claim:
 1. A chimeric protein capable of being incorporated into an HIV-1 or HIV-2 virion when expressed in trans with respect to the HIV-1 or HIV-2 genome comprising a first and a second portion, wherein said first portion has a Vpr/Vpx virion incorporation domain which includes the predicted N-terminal alpha helix of a viral protein selected from the group consisting of HIV-1 Vpr, HIV-2 Vpr, HIV-2 Vpx, SIV Vpr, and SIV Vpx; and wherein said Vpr/Vpx virion incorporation domain interacts with the p6 domain of Pr55^(gag), thereby enabling incorporation of said chimeric protein into said HIV-1 or HIV-2 virion.
 2. The chimeric protein of claim 1, wherein said viral protein is selected from the group consisting of HIV-1 Vpr, HIV-2 Vpr, and SIV Vpr.
 3. The chimeric protein of claim 2, wherein said viral protein is HIV-1 Vpr.
 4. The chimeric protein of claim 3, wherein said second portion is a polypeptide fragment covalently attached to the N- or C-terminus of said first portion.
 5. The chimeric protein of claim 4, wherein said polypeptide fragment comprises an amino acid sequence having RNAse or protease activity, whereby said RNAse or protease activity induces the degradation of RNA or protein inside said HIV-1 or HIV-2 virion.
 6. The chimeric protein of claim 4, wherein said polypeptide fragment comprises an amino acid sequence which prevents proper virion morphogenesis of said HIV-1 or HIV-2 virion.
 7. The chimeric protein of claim 2, wherein said first portion comprises an amino acid sequence that is selected from the group consisting of SEQ ID NO:1, SEQ ID NO:2, and SEQ ID NO:4.
 8. The chimeric protein of claim 4, wherein said polypeptide fragment is covalently attached to the C-terminus of said first portion.
 9. The chimeric protein of claim 8, wherein said polypeptide fragment comprises an amino acid sequence having RNAse or protease activity, whereby said RNAse or protease activity induces the degradation of RNA or protein inside said HIV-1 or HIV-2 virion.
 10. The chimeric protein of claim 8, wherein said polypeptide fragment comprises an amino acid sequence which prevents proper virion morphogenesis of said HIV-1 or HIV-2 virion.
 11. The chimeric protein of claim 8, wherein said first portion comprises the amino acid sequence of amino acids 1 to 72 of SEQ ID NO:1.
 12. The chimeric protein of claim 11, wherein said first portion comprises the amino sequence of amino acids 1 to 93 SEQ ID NO:1.
 13. The chimeric protein of claim 12, wherein said first portion comprises the amino acid sequence of SEQ ID NO:1.
 14. The chimeric protein of claim 1, wherein said viral protein is selected from the group consisting of HIV-2 Vpx, and SIV Vpx.
 15. The chimeric protein of claim 14, wherein said viral protein is HIV-2 Vpx having the amino acid sequence of SEQ ID NO:3.
 16. A composition for targeting into an HIV-1 or HIV-2 virion, which comprises an effective amount of the chimeric protein of claim 1 in association with a pharmaceutically acceptable carrier.
 17. A composition for targeting into an HIV-1 or HIV-2 virion, which comprises an effective amount of the chimeric protein of claim 2, in association with a pharmaceutically acceptable carrier.
 18. A composition for targeting into an HIV-1 or HIV-2 virion, which comprises an effective amount of the chimeric protein of claim 3 in association with a pharmaceutically acceptable carrier.
 19. A composition for targeting into an HIV-1 or HIV-2 virion, which comprises an effective amount of the chimeric protein of claim 8, with a pharmaceutically acceptable carrier.
 20. The chimeric protein of claim 1, wherein said second portion is a polypeptide fragment attached to the N- or C-terminus of said first portion.
 21. The chimeric protein of claim 11, wherein said polypeptide fragment comprises an amino acid sequence having RNAse or protease activity, whereby said RNAse or protease activity induces the degradation of RNA or protein inside said HIV-1 or HIV-2 virion.
 22. The chimeric protein of claim 11, wherein said polypeptide fragment comprises an amino acid sequence which prevents proper virion morphogenesis of said HIV-1 or HIV-2 virion.
 23. The chimeric protein of claim 1, wherein said first portion comprises an amino acid sequence selected from the group consisting of SEQ ID NO:1,
 24. The chimeric protein of claim 23, wherein said first portion comprises the amino acid sequence of amino acids 1 to 93 of SEQ ID NO:1.
 25. The chimeric protein of claim 23, wherein said first portion comprises the amino acid sequence of amino acids 1 to 72 of SEQ ID NO:1. 